Thermo Problems PDF

1\. A man has a mass of 75 kg. What is his weight in Newtons? 2\. Teacher John weighs 180 pounds. What is his mass in slug and in lbm? 3\. A woman has a mass of 54 kg on planet earth. What is the woman's mass on a planet whose gravity is 4 m/s2? 4\. An object weighs 52 pounds on earth. What would...

1\. A man has a mass of 75 kg. What is his weight in Newtons? 2\. Teacher John weighs 180 pounds. What is his mass in slug and in lbm? 3\. A woman has a mass of 54 kg on planet earth. What is the woman's mass on a planet whose gravity is 4 m/s2? 4\. An object weighs 52 pounds on earth. What would be the object's weight on the moon where the acceleration due to gravity is 1.67 m/s2? Express your answer in pound mass. 5\. What volume will 150 g of mercury occupy? Density of mercury is 13.6 g/cm3. 6\. A board measures 2\" x 6\" x 5\'. It weighs 15 lbs and 4 oz. Determine its weight density in lb/ft3. Notes in Thermodynamics − Vargas Page 3 7\. A vessel of volume 50 liters is filled with 2 kg of liquid water and 120 liters of steam with a specific volume of 0.02 m3/kg. Determine the density of the system (liquid water + steam). Answer in kg/m3 8\. A lubricating oil has a specific gravity of 0.92. Calculate its density in kg/m3. 9\. A cylinder of plastic is 100 mm long, and 50 mm in diameter. It has a mass of 1 kg. Determine its specific gravity. 10\. A woman's systolic blood pressure when resting is 160 mm Hg. What is this pressure in lb/in2? 11\. A gauge indicates 12 kPa as the fluid pressure while the outside pressure is 110 kPa. Determine the absolute pressure of the fluid in kPa. 12\. A vacuum gauge attached on a steam condenser indicates 65 kPa vacuum. The barometer indicates 1.013 bar. Determine the absolute pressure inside the condenser in kPa. 13\. What is the water pressure on the bottom of the sea at a depth of 3600 m? The specific gravity of sea water is assumed to be 1.03. 14\. A worker has a fever and her body temperature is 40°C. What is her temperature in oF? 15\. On a warm summer day, the air temperature is 85°F. What is its absolute temperature in Rankine? 16\. A room air conditioner causes a temperature change of −5.2°C. What is the temperature change in Kelvin? 17\. Water enters an electric heater at 30oC and leaves a t 38oC. What is the change in temperature in oF? 18\. A garden hose of inner radius 1.0 cm carries water at 2.0 m/s. The nozzle at the end has radius 0.20 cm. How fast does the water travel through the nozzle? 19\. One cubic meter per second of air enters a rectangular air duct measuring 200 mm by 150 mm with a density of 1.2 kg/m3. It leaves through another air duct measuring 175 mm by 125 mm with a density of 1.18 kg/m3. Calculate the volume flow rate of leaving air in m3/s 1\. A cylinder of plastic is 100 mm long, and 50 mm in diameter. It has a mass of 1 kg. Determine its specific gravity. 5.092 2\. What volume will 150 g of mercury occupy? Density of mercury is 13.6 g/cm3. 11.03 cm3 3\. A casting of an alloy in the form of a disk weighed 74 g. The disk was 0.125 inch thick and had a circular cross section of diameter 1.75 in. What is the density of the alloy in g/cm3? 15.028 g/cm3 4\. A submarine is constructed so that it can safely withstand a pressure of 1.2 × 107 Pa. How deep may this submarine descend in the ocean if the average density of seawater is 1026 kg/m3? 1193.5 m 5\. A condenser vacuum gage reads 706 mm Hg when the barometer stands at 755 mm Hg. State the absolute pressure in the condenser in bars 0.065 bars 6\. Express a pressure of 25 mm water in mm Hg. 1.84 mm Hg 7\. The gauge pressure of the air in an automobile tire is 0.21 lb/ft2. Convert this to torr. 0.075 torr 8\. The temperature of a furnace is estimated to be around 4500 oR. Express this temperature in oC. 2226.67 oC 9\. On a day when the temperature reaches 41oC, what is the temperature in Kelvin? 314 K 10\. A nurse measures the temperature of a patient to be 41oC. What is this temperature on the Fahrenheit scale? 105.8 oF 11\. The temperature difference between the inside and the outside of a home on a cold winter day is 54.0 oF. Express this difference on the Kelvin scale. 30 K 12\. Water enters a large pipe having a cross sectional area of 10 cm2 with a velocity of 1.2 m/s. A smaller pipe having a cross sectional area of 6 cm2 is connected to a large pipe. What is the velocity of water leaving the smaller pipe? 2 m/s 13\. A garden hose fills a 25-L wastebasket in 120 s. The opening at the end of the hose has a radius of 1.00 cm. How fast is the water travelling as it leaves the hose? 66.3 cm/s 14\. The heart pumps blood into the aorta, which has an inner radius of 1.0 cm. The aorta feeds 32 major arteries. If blood in the aorta travels at a speed of 25 cm/s, at approximately what average speed does it travel in the arteries? Assume that blood can be treated as an ideal fluid and that the arteries each have an inner radius of 0.20 cm 19.53 cm/s 1\. A person gets into an elevator at the lobby level of a hotel together with his 30-kg suitcase, and gets out at the 10th floor 35 m above. Determine the amount of energy consumed by the motor of the elevator that is now stored in the suitcase. A. 12.6 kJ B. 10.3 kJ C. 7.54 kJ D. 4.45 kJ 2\. A car of mass 1775 kg travels with a velocity of 100 km/h. How high should the car be lifted to have a potential energy that equals the kinetic energy? A. 23.5 m B. 28.1 m C. 32.6 m D. 39.3 m 3\. Calculate the total kinetic energy, in Btu, of an object with a mass of 10 lbm when its velocity is 50 ft/s. A. 0.50 Btu B. 0.84 Btu C. 1.92 Btu D. 2.65 Btu 4\. Determine the gravitational potential energy, in kJ, of 2 m3 of liquid water at an elevation of 30 m above the surface of Earth. Take the acceleration due to gravity as constant at 9.7 m/s2 and the density of the water is uniform at 1000 kg/m3. A. 347 kJ B. 465 kJ C. 582 kJ D. 658 kJ 5\. At a certain location, wind is blowing steadily at 10 m/s. Determine the mechanical energy of the wind, in kJ/s, blowing through a wind turbine with 30-m-diameter blades at that location. Take the air density to be 1.25 kg/m3. A. 1,620 kJ/s B. 1,050 kJ/s C. 758 kJ/s D. 442 kJ/s 1\. A bulldozer pushes 800 kg of dirt 100 m with a force of 1500 N. It then lifts the dirt 3 m up to put it in a dump truck. How much work did it do? A. 134 kJ B. 154 kJ C. 174 kJ D. 194 kJ 2\. Steam at 100°C is added to ice at 0°C. Find the amount of ice melted and the final temperature when the mass of steam is 10.0 g and the mass of ice is 50.0 g. A. 40.4 °C B. 44.0 °C C. 47.2 °C D. 51.5 °C Notes in Thermodynamics -- Vargas and Blones Page **9** of **18** 3\. A waterfall is 125 m high. What is the increase in water temperature at the bottom of the falls if all the initial potential energy goes into heating the water? A. 0.29 °C B. 0.46 °C C. 0.65 °C D. 0.90 °C 4\. A 650-kg elevator starts from rest. It moves upward for 3.00 s with constant acceleration until it reaches its cruising speed of 1.75m/s. What is the average power of the elevator motor during this period? A. 2.47 kW B. 3.65 kW C. 4.82 kW D. 5.91 kW 5\. Determine the power required for a 2000-kg car to climb a 100-m-long uphill road with a slope of 30° (from horizontal) in 10 s from rest to a final velocity of 30 m/s. A. 98.5 kW B. 146 kW C. 188 kW D. 238 kW 1\. A rigid tank contains a hot fluid that is cooled while being stirred by a paddle wheel. Initially, the internal energy of the fluid is 800 kJ. During the cooling process, the fluid loses 500 kJ of heat, and the paddle wheel does 100 kJ of work on the fluid. Determine the final internal energy of the fluid. \[Answer: 400 kJ\] 2\. A vertical piston--cylinder device contains water and is being heated on top of a range. During the process, 65 Btu of heat is transferred to the water, and heat losses from the side walls amount to 8 Btu. The piston rises as a result of evaporation, and 5 Btu of work is done by the vapor. Determine the change in the internal energy of the water for this process. \[**Answer: 52 Btu**\] 3\. During the winter, a house is projected to lose heat at a rate of 7.5 kJ/s. The internal heat gain from people, lights, and appliances is estimated to be 1.75 kJ/s. If this house is to be heated by electric resistance heaters, determine the energy consumed (in kWh) by the heaters per day to maintain the house at constant temperature. \[Answer: 138 kWh\] 4\. Suppose that the closed system executes a process for which 389 ft-lb of work was done on it while rejecting 1.5 Btu of heat. Find the change in internal energy. \[**Answer: −1.0 Btu**\] 5\. In the compression stroke of an internal combustion engine the heat rejected to the cooling water is 50 kJ/kg and the work input is 120 kJ/kg. Calculate the change in internal energy of the working fluid. \[Answer: 70 kJ/kg\] 1\. A nozzle receives 0.5 kg/s of air at a pressure of 2700 kPa and a velocity of 30 m/s and with an enthalpy of 923.0 kJ/kg, and the air leaves at a pressure of 700 kPa and with an enthalpy of 660 kJ/kg. Determine the exit velocity from the nozzle for flow where the heat loss is 1.3 kJ/kg \[Answer: **724.1 m/s**\] 2\. An air compressor handles 6.0 m3/min with a density of 1.25 kg/m3 and a pressure of 1 atm., and it discharges at 435 kPa (gage) with a density of 4.80 kg/m3. The change in specific internal energy across the compressor is 78 kJ/kg, and the heat loss by cooling is 25 kJ/kg. Neglecting changes in kinetic and potential energies, find the power in kW. \[Answer: **16.71 kW**\] 3\. A fluid at 700 kPa, with a specific volume of 0.25 m3/kg and a velocity of 170 m/s, enters a device. Heat loss from the device by radiation is 23 kJ/kg. The work done by the fluid is 468 kJ/kg. The fluid exits at 136 kPa, 0.94 m3/kg, and 335 m/s. Determine the change in internal energy. \[Answer: **−485.5 kJ/kg**\] 4\. A steam condenser receives 9.47 kg/s of steam with an enthalpy of 2570 kJ/kg. The steam condenses to a liquid and leaves with an enthalpy of 160.5 kJ/kg. Find the total heat transferred from the steam. \[Answer: **22,818 kW**\] 5\. Steam enters a turbine at 20 m/s and specific enthalpy of 3000 kJ/kg and leaves the turbine at 40 m/s and specific enthalpy of 2500 kJ/kg. Heat lost to the surroundings is 25 kJ/kg of steam as the steam passes through the turbine. If the steam flow rate is 360,000 kg/h, determine the output from the turbine in MW. \[Answer: **47.44 MW**\] 3.1. What is the volume of 3 kg of an ideal gas, having a gas constant of 287 J/(kg K) at a pressure of 1 atm and at 26°C? **\[2.54 m3\]** 3.2. 88 grams of CO2 at 27OC is having a 5 atm pressure. What is the volume occupied by it? \[9.8 liters\] 3.3. Determine the new pressure in the rigid container when a gas at 1.08 bar is heated from 20.0 °C to 40.0 °C. **\[1.15 bar\]** 3.4. A mass of an ideal gas occupies 1.0 m3 at 25°C and is heated at constant pressure to 120°C. What is the final volume, in m3? **\[1.32 m3\]** 3.5. A gas occupies 106.3 liters at a pressure of 840 mmHg. What is the volume when the pressure is increased to 1260 mmHg? **\[70.87 liters\]** 3.6. The pressure, volume and temperature of a 10 kg gas, change from 1 bar absolute, 1.25 m3 and 50°C respectively to 4 bar absolute and 0.5 m3. Find its final temperature, in °C. **\[243.8°C\]** 3.7. The gas constant of an unknown gas is 270 J/(kg K) and its specific heat at constant volume is 800 J/(kg K). Find its specific heat at constant pressure. **\[1070 J/kg-K\]** 3.8. The specific heat ratio of air is 1.4. If its specific heat at constant pressure is 1.005 kJ/(kg K), what is its specific heat at constant volume? **\[0.72 kJ/kg K\]** **3.9. What is the gas constant of gas having Cp = 1325 ft-lbf/(lbm-R) and k = 1.3?** **\[305.77 ft-lbf/lbm-R\]** **3.10. One kg of air at 20°C is heated until its temperature is 150°C. What is the change of its internal energy? Cv of air is 0.728 kJ/(kg C).** **\[94.64 kJ\]** **3.11 Five kg of oxygen is cooled from 40°C to 20°C. What is the change of its enthalpy? Cp of oxygen is 0.918 kJ/(kg K).** **\[−91.8 kJ\]** 1\. Two cubic meters of air at 24oC and 2070 kPa abs are compressed isothermally to a pressure of 6207 kPa abs. The specific heats of air are Cp = 1.005 kJ/kg-K and Cv = 0.718 kJ/kg-K. What would be (a) the final volume, (b) the change of internal energy, (c) the change of enthalpy, (d) the non-flow work, (e) the steady flow work (f) the heat transferred, and (g) the change of entropy. *\[(a) 0.667 m3, (b) 0, (c) 0, (d) ‒4546.2 kJ, (e) ‒4546.2 kJ, (f) ‒4546.2 kJ, (g) ‒15,307 J/K\]* **Sample Problem 4.2** Oxygen having a volume of 20 ft3 change state at constant pressure at 100 psi until the volume becomes 10 ft3. For oxygen, R = 0.062 Btu/lbm-R and k = 1.395. If the initial temperature is 86oF, find (a) the final temperature, (b) the change of internal energy, (c)the change of enthalpy, (d) the non-flow work, (e) the steady flow work, (f)the heat transferred, (g) the change of entropy. *\[(a) ‒187oF, (b) ‒468.6 Btu, (c) ‒653.5 Btu, (d) ‒185.0 Btu (e) 0 (f) ‒653.5 Btu, (g) ‒1.66 Btu\]* **Sample Problem 4.3** Ten cubic meters of hydrogen at a pressure of 2069 kPaa and a temperature of 204oC is cooled to 60oC at constant volume. The gas constant of hydrogen is 4.125 kJ/kg K and its specific heat ratio is 1.4. What is (a) the final pressure, (b) the change of internal energy, (c) the change of enthalpy (d) the non-flow work, (e) the steady flow work (f) the transferred heat, (g) the change of entropy. *\[(a) 1444.4 kPa, (b) ‒15,618 kJ, (c) ‒21,867 kJ, (d) 0, (e)* 6,246 𝑘𝐽, *(f) ‒15,618 kJ,* *(g) ‒38.94 kJ/K\]* Sample Problem 4.4 Three cubic meters of carbon dioxide, considered as a perfect gas, are compressed isentropically from 1930 kPa and 40oC to 5579 kPa. Find (a) final temperature, (b) final volume, (c) the change of internal energy, (d) the change of enthalpy, (e) the non-flow work, (f) the steady-flow work, (g) the heat transferred (h) the change of entropy. For carbon dioxide, R = 0.1889 kJ/(kg-K) and k = 1.289. Sample Problem 4.5 Air is expanded according to the relation PV1.33 = C in a non-flow process from a pressure of 1414 kPa abs to 174.5 kPa abs. If the initial volume and temperature are 0.0354 m3 and 29oC respectively, what is (a) the final temperature, (b) the change of internal energy, (c) the change of enthalpy (d) the work, (e) the transferred heat, (f) the change of entropy? Example 5.1 Determine the thermal efficiency of a heat engine which rejects 200 kJ of heat to a low temperature sink and has a work output of 80 kJ. Example 5.2 Heat is transferred to a heat engine from a furnace at a rate of 80 MW. If the rate of waste heat rejection to a nearby river is 50 MW, determine the net power output and the thermal efficiency for this heat engine. Example 5.3 A car engine with a power output of 65 hp has a thermal efficiency of 24 percent. Determine the fuel consumption rate of this car if the fuel has a heating value of 19,000 Btu/lbm (that is, 19,000 Btu of energy is released for each lbm of fuel burned). Example 5.4 A household refrigerator runs one-fourth of the time and removes heat from the food compartment at an average rate of 800 kJ/h. If the COP of the refrigerator is 2.2, determine the power the refrigerator draws when running. Example 5.5 The food compartment of a refrigerator is maintained at 4°C by removing heat from it at a rate of 360 kJ/min. If the required power input to the refrigerator is 2 kW, determine (a) the coefficient of performance of the refrigerator and (b) the rate of heat rejection to the room that houses the refrigerator. Example 5.6 A heat pump is used to meet the heating requirements of a house and maintain it at 20°C. On a day when the outdoor air temperature drops to 2°C, the house is estimated to lose heat at a rate of 80,000 kJ/h. If the heat pump under these conditions has a COP of 2.5, determine (a) the power consumed by the heat pump and (b) the rate at which heat is absorbed from the cold outdoor air. 5.1. A Carnot engine produces 25 kW while operating between temperature limits of 1000oK and 300oK. Determine (a) the heat supplied per second; (b) the heat rejection per second. 5.2. A Carnot cycle uses nitrogen as the working substance. The heat supplied is 54 kJ. The temperature of the heat rejected is 21oC, and V3/V2 = 10. Determine (a) the cycle efficiency (b) the temperature of heat added, (c) the work. 5.3. Air is used in a Carnot engine where 22 kJ of heat is received at 560oK. Heat is rejected at 270oK. The displacement volume is 0.127 m3. Determine (a) the work (b) the mean effective pressure. 5.4. A reversed Carnot engine receives 316 kJ of heat. The reversible adiabatic compression process increases by 50% the absolute temperature of heat addition. Determine (a) the COP, (b) the work. 5.5. A heat pump is sued to heat a house in the winter months. When the average outside temperature temperature is 0oC and the indoor temperature is 23oC, the heat loss from the house is 20 kW. Determine the minimum power required to operate the heat pump. 5.6. A Carnot heat engine rejects 230 kJ of heat at 25oC. The net cycle work is 375 kJ. Determine the thermal efficiency and the cycle high temperature. 5.7. A refrigerator on the reversed Carnot cycle provides a refrigerated space at 4oC while in a room at 25oC. A wattmeter supplying power to the refrigerator reads 3.0 kW. What is the amount of cooling being provided? 5.8. A Carnot refrigerator, consuming 3.0 kW, is located in a room where the air temperature is 25oC. The COP is found to be 5.0. Determine the temperature of and the amount of heat removed from the refrigerated space. 5.9. it is desired to double the COPC of a reversed Carnot engine from 5.0 by raising the temperature of heat addition for a fixed high temperature. By what percentage must the low temperature be raised? 5.10. A building is heated by a heat pump and must be maintained at 20oC. The power to the heat pump is 8 kW, and the heat loss from the building is 29,000 kJ/h for each degree in temperature difference between the inside and the outside. Determine the lowest outside temperature possible, subject to the heating requirements. 5.11. A Carnot engine receives 100 kW at 1000oK and rejects heat to the surroundings at 300oK. The work from the engine is used to drive a reversed Carnot engine that operates between −20oC and 300oK. Determine the (a) the heat input to the reversed engine, (b) the total heat from both engines rejected to the environment at 300oK. 5.12. A reversed Carnot engine operating as a heat pump consumes 6 kW and has a COPH of 3.0. A house containing 1800 kg of air is initially at 12oC, and the heat raises the air temperature to 21oC. How long will this take. 6.1 A Carnot engine working between 400°C and 40°C produces 130 kJ of work. Determine: \(a) The engine thermal efficiency. \(b) The change of entropy \(c) The heat added. **Problem 6.2** 0.5 kg of air (ideal gas) executes a Carnot power cycle having a thermal efficiency of 50 per cent. The heat transfer to the air during the isothermal expansion is 40 kJ. At the beginning of the isothermal expansion the pressure is 7 bar and the volume is 0.12 m3. Determine: \(a) The maximum and minimum temperatures for the cycle in K \(b) The volume at the end of isothermal expansion in m3; \(c) The heat transfer for each of the four processes in kJ. **Problem 6.3** In a Carnot cycle, the maximum pressure and temperature are limited to 18 bar and 410°C. The ratio of isentropic compression is 6 and isothermal expansion is 1.5. Assuming the volume of the air at the beginning of isothermal expansion as 0.18 m3, determine: \(a) The temperature and pressures at main points in the cycle. \(b) Change in entropy during isothermal expansion. \(c) Mean thermal efficiency of the cycle. \(d) Mean effective pressure of the cycle. \(e) The theoretical power if there are 210 working cycles per minute. Problem 4 A reversed Carnot cycle is used for heating and cooling. The work supplied is 10 kW. If the COP = 3.5 for cooling, determine (a) TH/TL (b) the refrigerating effect in tons of refrigeration, (c) the COP for heating. **Problem 7.1** The compression ratio in an air-standard Otto cycle is 10. At the beginning of the compression stoke, the pressure is 0.1 MPa and the temperature is 15◦C. The heat transfer to the air per cycle is 1800 kJ/kg air. Determine A. The pressure and temperature at the end of each process of the cycle. B. The heat added in the cycle C. The heat rejected in the cycle D. The thermal efficiency. E. The mean effective Problem 8.1 At the beginning of the compression process of an air-standard Diesel cycle operating with a compression ratio of 18, the temperature is 300 K and the pressure is 100 kPa. The cutoff ratio for the cycle is 2. Determine (a) the temperature and pressure at the end of each process of the cycle, (b) the heat added, (c) the heat rejected, (d) the net work, (e) the thermal efficiency, (f) expansion ratio, (g) the volume displacement, \(h) the mean effective pressure, in kPa. 1\. A perfect gas has a value of R = 2.08 kJ/kg-K and k = 1.659. If 527 kJ of heat are added to 2.27 kg of this gas at constant pressure when the initial temperature is 38oC, find the change of enthalpy. A. 527 kJ B. 606 kJ C. 455 kJ D. 306 kJ 2\. Air having a mass of 1.8 kg are compressed isothermally from 90 kPa and volume of 1.134 m3 to 483 kPa. Find the work. A. ‒171.5 kJ B. ‒235.7 kJ C. ‒94.6 kJ D. ‒352.8 kJ 3\. Five cubic meter of nitrogen are heated at constant volume so that the pressure changes from 276 kPaa to 1375 kPa gage. For nitrogen, R = 0.296 kJ/kg-K and Cp = 1.039 kJ/kg-K. Find the change of internal energy. A. 15,065 kJ B. 16,700 kJ C. 17,825 kJ D. 18,575 kJ 4\. Air having a mass of 1.8 kg are compressed isothermally from 90 kPa and volume of 1.134 m3 to 483 kPa. Find the change of entropy. A. −0.868 kJ/K B. −1.255 kJ/K C. −2.388 kJ/K D. −3.406 kJ/K 5\. From 400 kPa abs and 0.8 m3, air is being compressed isentropically to 0.5 m3. Find the change of internal energy. A. 165.5 kJ B. 128.1 kJ C. 144.9 kJ D. 180.7 kJ 6\. A gas (composition not known) is cooled at constant volume of 0.85 m3 from 593 kPa abs. and 60oC to 138oC. Determine the heat transferred if the value of R = 0.744 kJ/kg-K and k = 1.4? A. 295.2 kJ B. 352.4 kJ C. 215.6 kJ D. 334,8 kJ 7\. One kg of air at 207 kPa and 26.7oC has its temperature raised to 27.2oC while the pressure is constant. Find the work done in J. A. 142.5 J B. 206.5 J C. 303.7 J D. 424.1 J 8\. Oxygen at 50oC and 0.5 m3 expands to 1.0 m3 at constant entropy. If the specific heat ratio for oxygen is 1.395 what is the final temperature? A. 245.6K B. 288.4K C. 226.2K D. 298.7K 9\. Three kg of air at 31oC and 350 kPa undergo an isothermal process until the pressure becomes 100 kPa. Find the heat transferred. A. 327.9 kJ B. 182.6 kJ C. 205.4 kJ D. 308.5 kJ 10\. During a non-flow isentropic process of 1.7 kg of air, the temperature decreases from 80oC to 35oC. Find the work. A. 54.9 kJ B. 60.7 kJ C. 48.8 kJ D. 70.4 kJ 11\. Five kg of air at 100 kPa and 25oC are compressed according to the law PV1.3 = C until its pressure reaches 350 kPa. Find the change of entropy. R and Cp of air are 0.287 and 1.005 kJ/kg-K respectively. A. ‒0.345 kJ/K B. ‒0.516 kJ/K C. ‒1.022 kJ/K D. ‒1.315 kJ/K 12\. A perfect gas has a value of R = 2.08 kJ/kg-K and k = 1.659. If 527 kJ of heat are added to 2.27 kg of this gas at constant pressure when the initial temperature is 38oC, find the change of internal energy. A. 317.4 kJ B. 266.3 kJ C. 428.5 kJ D. 518 kJ 13\. The pressure on 10 ft3 of air is raised from 15 to 75 psi abs while the volume is unchanged. What is the steady flow work? A. 216,300 ft-lbf B. ‒86,400 ft-lbf C. 302,800 ft-lbf D. ‒144,500 ft-lbf 1\. A car engine with a power output of 110 hp has a thermal efficiency of 28 percent. Determine the rate of fuel consumption if the heating value of the fuel is 19,000 Btu/lbm. A. 0.622 lb/min B. 0.877 lb/min C. 0.287 lb/min D. 0.487 lb/min 2\. A window-mounted air-conditioner unit is placed on a laboratory bench and tested in cooling mode using 750 W of electric power with a COP of 1.75. What is the cooling power capacity? A. 1313W B. 1044W C. 1518W D. 1747W 3\. A heat engine has a heat input of 3 x 104 Btu/h and a thermal efficiency of 40 percent. Calculate the power it will produce, in hp. A. 6.17 hp B. 3.28 hp C. 5.65 hp D. 4.72 hp 4\. An industrial machine is being cooled by 0.4 kg/s water at 15◦C that is chilled from 35◦C by a refrigeration unit with a COP of 3. Find the rate of cooling required. A. 27.5 kW B. 46.5 kW C. 33.5 kW D. 50.5 kW 5\. The thermal efficiency of a general heat engine is 35 percent, and it produces 60 hp. At what rate is heat transferred to this engine, in kJ/s? A. 127.9 kJ/s B. 204.5 kJ/s C. 348.6 kJ/s D. 462.2 kJ/s 6\. A window air conditioner discards 1.7 kW to the ambient with a power input of 500 W. Find the COP. A. 3.7 B. 2.4 C. 2.8 D. 3.1 7\. A 600-MW steam power plant, which is cooled by a nearby river, has a thermal efficiency of 40 percent. Determine the rate of heat transfer to the river water. A. 240 MW B. 2400 MW C. 900 MW D. 800 MW 8\. The refrigerator in a kitchen receives electrical input power of 150 W to drive the system, and it rejects 400 W to the kitchen air. Find the COP of the refrigerator. A. 1.33 B. 2.00 C. 2.25 D. 1.67 9\. A heat engine that pumps water out of an underground mine accepts 700 kJ of heat and produces 250 kJ of work. How much heat does it reject, in kJ? A. 950 kJ B. 600 kJ C. 450 kJ D. 500 kJ 10\. A room is heated with a 1500-W electric heater. How much power can be saved if a heat pump with a COP of 2.5 is used instead? A. 750 W B. 900 W C. 500 W D. 650 W 1\. What is the highest possible theoretical efficiency of a heat engine operating with a hot reservoir of furnace gases at 2100°C when the cooling water available is at 15°C? A. 72.5% B. 87.9% C. 64.8% D. 53.1% 2\. A domestic food freezer maintains a temperature of --15°C. The ambient air temperature is 30°C. If heat leaks into the freezer at the continuous rate of 1.75 kJ/s what is the least power necessary to pump this heat out continuously. A. 1.38 kW B. 0.74 kW C. 1.63 kW D. 0.31 kW 3\. A Carnot cycle operates between source and sink temperatures of 250°C and --15°C. If the system receives 90 kJ from the source, find the net work. A. 52.6 kJ B. 45.6 kJ C. 63.2 kJ D. 38.2 kJ 4\. A refrigerating machine works on a reversed Carnot cycle. It consumes 6 kW and the refrigerating effect is 1000 kJ/min. The sink temperature is -- 40°C. Determine the source temperature. A. 54.6oC B. 63.2oC C. 76.5oC D. 43.8oC c5. A cyclic heat engine operates between a source temperature of 1000°C and a sink temperature of 40°C. Find the least rate of heat rejection per kW net output of the engine? A. 0.415 kW B. 0.244 kW C. 0.288 kW D. 0.326 kW 6\. A house is to be maintained at 25°C in winter. For this purpose, it is proposed to use a reversible device as a heat pump in winter. The ambient temperature is 3°C in winter. The energy losses as heat from the roof and the walls are estimated at 5 kW per degree Celsius temperature difference between the room and the ambient conditions. Calculate the power required to operate the device in winter. A. 6.53 kW B. 7.44 kW C. 5.81 kW D. 8.12 kW 9.1 Air enters the compressor of an ideal air-standard Brayton cycle at 100 kPa, 300 K, with a volumetric flow rate of 5 m3/s. The compressor pressure ratio is 10. The turbine inlet temperature is 1400 K. Determine (a) the thermal efficiency of the cycle, (b) the back work ratio, (c) the net power developed, in kW a\. 48.2% b. 0.41 c. 2309.4 kW